1. Field of the Invention
The present invention relates to an improved saw tooth for circular saws, and more particularly, to a saw tooth with multiple cutting edges which can be replaced when the active cutting edges become dull or worn.
2. Description of the Prior Art
Saw teeth for circular saws of the type mounted on a feller head for a tree felling apparatus have undergone considerable change in the last few years.
U.S. Pat. No. 4,932,447, Morin, 1990, and U.S. Pat. No. 5,205,199, MacLennan, 1993, represent saw teeth which have become the standards in the industry- When the active cutting tips and edges become dull or worn, these saw teeth can be rotated to present different tips and cutting edges. In fact, the principle of rotating a saw tooth to present different cutting edges on a saw tooth was proposed as far back as 1956 in U.S. Pat. No. 2,736,352 by Wright and in 1980 by Jonsson in U.S. Pat. No. 4,231,406. The Wright patent describes a frusto-conical tooth for chain saws or circular saws presenting annular cutting edges which can be rotated to present a fresh cutting edge segment. The Jonsson patent describes a replaceable debarking tooth having four sides which can be rotated 90.degree. to present a sharp cutting edge when the previous edge has become dull.
Morin '447 and MacLennan '199 both show replaceable saw teeth with four sides which can be rotated. The MacLennan patent provides V-shaped cutting edges with four planar surfaces defining cutting tips at the apex of these somewhat triangular surfaces. Flat triangular carbide inserts may overlie the flat surfaces to reinforce the cutting edges. These inserts are brazed to the tooth head. Morin '447 describes a four-sided tooth with concavely curved cutting edges formed by a spherical concave recess. Four cutting tips are present, one at each corner. In both MacLennan and Morin, it is necessary to rotate the tooth to provide sharp fresh tips and cutting edges.
Although theoretically the MacLennan or Morin teeth can be rotated four times before replacement, it is probably not practical. In fact, the most that such teeth can be rotated is three times. In practice, the active edge (remote from the center of the saw blade) of the tooth and the two adjacent tips are blunted by wear. In fact, the lower tip of the remote edge, when the tooth is mounted on the saw blade, is more susceptible to being blunted since it is the closest to the ground and more likely to hit a solid obstacle such as stones or sand. If this lower tip is blunted, it cannot be reused with another adjacent edge. Likewise, if the two tips adjacent the outer edge are blunted equally by wear or impact, then the tooth can only be rotated by 180.degree., that is, twice.